docs: def _ensure_sequence(self, mutable=False):
          """This method can be called by methods that need a sequence.  If
          `mutable` is true, it will also ensure that the response sequence
          is a standard Python list.
  
          .. versionadded:: 0.6
          """
          if self.is_sequence:
              # if we need a mutable object, we ensure it's a list.
              if mutable and not isinstance(self.response, list):
                  self.response = list(self.response)
              return
          if self.direct_passthrough:
              raise RuntimeError('Attempted implicit sequence conversion '
                                 'but the response object is in direct '
                                 'passthrough mode.')
          if not self.implicit_sequence_conversion:
              raise RuntimeError('The response object required the iterable '
                                 'to be a sequence, but the implicit '
                                 'conversion was disabled.  Call '
                                 'make_sequence() yourself.')
          self.make_sequence()